When you go outside, you might notice people, grass, flowers, birds, and insects. You also are probably aware of nonliving things, such as air, sunlight, and water. The living or once-living parts of an environment are the biotic parts. The nonliving parts that the living parts need to survive are the abiotic parts. The biotic and abiotic parts of an environment together make up an ecosystem.

Earth’s continents have many different ecosystems, from deserts to rain forests. Scientists classify similar ecosystems in large geographic areas as biomes. Abiomeis a geographic area on Earth that contains ecosystems with similar biotic and abiotic features.As shown in Figure 1,Earth has seven major land biomes. Areas classified as the same biome have similar climates and organisms.

Figure 1Earth contains seven major biomes.

Biodiversity in Ecosystems and Biomes

The abiotic factors in each major land biome determine which organisms can live in those ecosystems. The organisms that live in deserts might not survive in tropical rain forests. However, each biome supports a variety of species. The number of different species in an area is its biodiversity. The greater the biodiversity in an ecosystem, the more likely that ecosystem will be sustainable.

Grasslandbiomes are areas where grasses are the dominant plants.Also called prairies, savannas, and meadows, grasslands are the world’s “breadbaskets.” Wheat, corn, oats, rye, barley, and other important cereal crops are grasses. They grow well in these areas.

• Grasslands have a wet and a dry season.

• Deep, fertile soil supports plant growth.

• Grass roots form a thick mass, called sod, which helps soil absorb and hold water during periods of drought.

1.Reading CheckWhy are grasslands called “breadbaskets”?

Biodiversity

• Trees grow along moist banks of streams and rivers. Wildflowers bloom during the wet season.

• In North America, large herbivores, such as bison and elk, graze here. Insects, birds, rabbits, prairie dogs, and snakes find shelter in the grasses.

• Predators in North American grasslands include hawks, ferrets, coyotes, and wolves.

• African savannas are grasslands that contain giraffes, zebras, and lions. Australian grasslands are home to kangaroos, wallabies, and wild dogs.

Laura Romin & Larry Dalton/Alamy

Human Impact

• People plow large areas of grassland to raise cereal crops. This reduces habitat for wild species.

• Because of hunting and loss of habitat, large herbivores—such as bison—are now uncommon in many grasslands.

Regions of Earth between the tropics and the polar circles aretemperateregions.Temperate regions have relatively mild climates with distinct seasons. Several biomes are in temperate regions, including rain forests. Temperate rain forests are moist ecosystems mostly in coastal areas. They are not as warm as tropical rain forests.

• Winters are mild and rainy.

• Summers are cool and foggy.

• Soil is rich and moist.

Biodiversity

• Forests are dominated by spruce, hemlock, cedar, fir, and redwood trees, which can grow very large and tall.

Temperate deciduous forests grow in temperate regions where winter and summer climates have more variation than those in temperate rain forests. These forests are the most common forest ecosystems in the United States. They contain mostly deciduous trees, which lose their leaves in the fall.

• Winter temperatures are often below freezing. Snow is common.

• Summers are hot and humid.

• Soil is rich in nutrients and supports a large amount of diverse plant growth.

(t) Tom Till

Biodiversity

• Most plants, such as maples, oaks, birches, and other deciduous trees, stop growing during the winter and begin growing again in the spring.

Ataiga (TI guh) is a forest biome consisting mostly of cone-bearing evergreen trees.The taiga biome exists only in the northern hemisphere. It occupies more space on Earth’s continents than any other biome.

• Winters are long, cold, and snowy. Summers are short, warm, and moist.

Some types of aquatic ecosystems have mostly shallow water. Wetlandsare aquatic ecosystems that have a thin layer of water covering soil that is wet most of the time. Wetlands contain fresh water, salt water, or both. They are among Earth’s most fertile ecosystems.

• Freshwater wetlands form at the edges of lakes and ponds and in low areas on land. Saltwater wetlands form along ocean coasts.

Estuaries (ES chuh wer eez) are regions along coastlines where streams or rivers flow into a body of salt water. Most estuaries form along coastlines, where freshwater in rivers meets salt water in oceans. Estuary ecosystems have varying degrees of salinity.

• Salinity depends on rainfall, the amount of freshwater flowing from land, and the amount of salt water pushed in by tides.

• Estuaries help protect coastal land from flooding and erosion. Like wetlands, estuaries purify water and filter out pollution.

• Nutrient levels and biodiversity are high.

Tom & Therisa Stack/Tom Stack & Associates

Biodiversity

• Plants that grow in salt water include mangroves, pickleweeds, and seagrasses.

• Animals include worms, snails, and many species that people use for food, including oysters, shrimp, crabs, and clams.

• Striped bass, salmon, flounder, and many other ocean fish lay their eggs in estuaries.

• Many species of birds depend on estuaries for breeding, nesting, and feeding.

B. Moose Peterson

Human Impact

• Large portions of estuaries have been filled with soil to make land for roads and buildings.

• Destruction of estuaries reduces habitat for estuary species and exposes the coastline to flooding and storm damage.

Most of Earth’s surface is covered by ocean water with high salinity. The oceans contain different types of ecosystems. If you took a boat trip several kilometers out to sea, you would be in the open ocean—one type of ocean ecosystem. The open ocean extends from the steep edges of continental shelves to the deepest parts of the ocean. The amount of light in the water depends on depth.

• Photosynthesis can take place only in the uppermost, or sunlit, zone. Very little sunlight reaches the twilight zone. None reaches the deepest water, known as the dark zone.

• Decaying matter and nutrients float down from the sunlit zone, through the twilight and dark zones, to the seafloor.

(b) Camille Lusardi/Photolibrary

Biodiversity

• Microscopic algae and other producers in the sunlit zone form the base of most ocean food chains. Other organisms living in the sunlit zone are jellyfish, tuna, mackerel, and dolphins.

• Many species of fish stay in the twilight zone during the day and swim to the sunlit zone at night to feed.

• Sea cucumbers, brittle stars, and other bottom-dwelling organisms feed on decaying matter that drifts down from above.

• Many organisms in the dark zone live near cracks in the seafloor where lava erupts and new s eafloor forms.

1.Reading CheckWhich organisms are at the base of most ocean food chains?

Gregory Ochocki/Photo Researchers

Human Impact

• Overfishing threatens many ocean fish.

• Trash discarded from ocean vessels or washed into oceans from land is a source of pollution. Animals such as seals become tangled in plastic or mistake it for food.

9.Where would you find plants with stems that can store large amounts of water?

A.desert

B.grassland

C.taiga

D.tundra

10.What does the pink area on the map below represent?

A.taiga

B.tundra

C.temperate deciduous forest

D.temperate rain forest

11.Where would you find trees that have no leaves during the winter?

A.estuary

B.tundra

C.temperate deciduous forest

D.temperate rain forest

12Which biomes have rich, fertile soil?

A.grassland and taiga

B.grassland and tundra

C.grassland and tropical rain forest

D.grassland and temperate deciduous forest

13.Which ecosystem contains both salt water and freshwater?

A.estuary

B.lake

C.pond

D.stream

14.Describewhat might happen to a coastal area if its estuary were filled in to build houses.

15.Which is NOT a freshwater ecosystem?

A.oceans

B.ponds

C.rivers

D.streams

16.Where would you find species adapted to withstand strong wave action?

A.estuaries

B.wetlands

C.intertidal zone

D.twilight zone

17.Which ecosystem has flowing water?

A.estuary

B.lake

C.stream

D.wetland

18.Which ecosystems help protect coastal areas from flood damage?

A.estuaries

B.ponds

C.rivers

D.streams

Interpret Graphics

119.DetermineWhat is the average annual rainfall for the biome represented by the chart below?

20.Summarize InformationCopy the graphic organizer below and fill it in with animals and plants of the biome you live in.

Critical Thinking

21.Briefly describe the characteristics of Earth's seven major land biomes. List examples of plants and animals that live in each biome.

22.Planan enclosed zoo exhibit for a desert ecosystem. What abiotic factors should you consider?

23.Recommendone or more actions people can take to reduce habitat loss in tropical and taiga forests.

24.Comparemammals that live in tundra biomes with those that live in desert biomes. What adaptations does each group have that help them survive?

25.AnalyzeYou are invited to go on a trip to South America. Before you leave, you read a travel guide that says the country you will be visiting has hot summers, cold winters, and many wheat farms. What biome will you be visiting? Explain your reasoning.

26.Interpret GraphicsThe following climate data were recorded for a forest ecosystem. To which biome does this ecosystem likely belong?

27.Earth contains a wide variety of organisms that live in different conditions. How do Earth’s biomes and ecosystems differ?

28.Observe two biomes. How do the different environments of these biomes support different varieties of organisms? Explain.